In Dawn of Fantasy main directory.
Mithrill.dll rename to Mithrill.dll.old
Towns.mithpak rename to Towns.mithpak.old
Re-run Validation. The files will be re-aquired.
Could also behoove you to add firewall exceptions to DOF.exe, Towns.mithpak and Mithrill.dll before the validation.
PM me if you need more direct support.
For safe measure and less variables to the issue, repeat the linked steps that Zvonzi posted.